Preparation for test 1. Check, and correct, if necessary oil level in reservoir. 2. Remove plastic cover over hydraulic unit. 3. For test step 3.0, connect socket box according to connection diagram, figure 5.

Test step	Test scope	Test connection	Test condition	Nominal value	Possible cause/Remedy
1.0	Central differential lock multi-disc clutch (ZS) Engagement pressure	Service valve in "TEST" position or release accumulator pressure at screw plug (16). 250 bar gauge connected to "ZS" (Fig. 1-3)	Engine: at idle Service valve in operating position or switch (S7/3) in "FUNKTION" position.	25 - 36 bar	Central differential lock valve (A7/2y2), 4MATIC hydraulic unit (A7/2).
2.0	Front axle drivetrain multi-disc clutch (AV) Engagement pressure	Service valve in "TEST" position or release accumulator pressure at screw plug (16). 250 bar gauge connected to "AV" on hydraulic unit (Fig. 1-3)	Engine: at idle Service valve in operating position or switch (S7/3) in "FUNKTION" position.	25 - 36 bar	Front axle drivetrain valve (A7/2y1), 4MATIC hydraulic unit (A7/2).
3.0	Rear axle differential lock multi-disc clutch (HS) Engagement pressure	Service valve in "TEST" position or release accumulator pressure at screw plug (16). 250 bar gauge connected to "HS" (Fig. 1-3) 2 8	Ignition: OFF Unplug 4MATIC control module (N30/2) Engine: at idle Service valve in operating position or switch (S7/3) in "FUNKTION" position.	25 - 36 bar	Rear axle differential lock valve (A7/2y3), 4MATIC hydraulic unit (A7/2).
4.0 only vehicles up to 04/91	Front axle drivetrain multi-disc clutch (AV) Application pressure	Service valve in "TEST" position. 10 bar gauge connected to "AV" on hydraulic unit (Fig. 1, 5)	Ignition: OFF Unplug 4MATIC control module (N30/2) Engine: at idle Service valve in operating position	approx. 1.3 bar	4.1
4.1	Return line N Residual pressure	Service valve in "TEST" position. On vehicles with level control: level control valve in position "L", Fig. 6 10 bar gauge connected between "N" on hydraulic unit and disconnected line (Fig. 1, 4)	Engine: at idle Service valve in operating position	5 - 6 bar	Service valve. If pressure is reached: 4MATIC hydraulic unit (A7/2).